LAND AND MARINE: - PUSHING THE BOUNDARIES OF LARGE DIAMETER HDPE PIPES TO ENGINEERING EXTREMES

Authors

Simon Thomas MBA Simon Thomas Consulting Limited

Cardiff United Kingdom

Dr Vasilios Samaras CEng FIMechE IntPE(UK) Eur Ing Senior Lecturer

College of Engineering Swansea University

United Kingdom

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LAND AND MARINE: - PUSHING THE BOUNDARIES OF LARGE DIAMETER HDPE PIPES TO ENGINEERING EXTREMES

Abstract

High Density Polyethylene HDPE pipes provide to the designers, owners and contractors a reliable, long term service durability and cost-effective solution for a wide range of piping applications including gas, municipal, industrial, storm water attenuation, mining, landfill and electrical and communications duct applications. HDPE pipes are also effective for above ground, trenchless, floating and marine installations. Add to the above the potential of a very low maintenance and the easy installation compared to traditional materials and plastic pipe is a very competitive product.

In the last few years, large diameter HDPE pipes have witnessed greater acceptance and strong growth in usage, particularly within the water industry, when innovation combined with best value is an absolute necessity; and research suggests they can contribute significantly towards achieving this aim on major turnkey projects in the construction industry. The current work includes case studies for major schemes in the United Kingdom worldwide. It includes case study of a 10000 m3 flood alleviation scheme constructed in 2600mm internal diameter Structured Wall HDPE pipe and installed in Scotland, 2200 & 2400mm intake and outfall pipelines for a major refinery in Asia are included and finally, an innovative installation for a 3000mm diameter marine outfall in London. The main scope of the present work is to illustrate the distinct advantage of large plastic pipes in comparison to traditional materials demonstrating the versatility, creativity and innovation that can be achieved with their use and to illustrate the positive impact and contribution that modern plastics have on society in general.

Introduction In the last two years, plastic has become the enemy of people everywhere. Headlines such as this “The plastic backlash: what's behind our sudden rage – and will it make a difference?”1 and “Plastic (not) fantastic: Why even biodegradable plastic can still harm the environment”2 are commonplace. Indeed, one writer suggests that plastics was generally anonymous until very recently. It is unfortunate that plastic has become a victim of its own apathy. The industry is guilty of standing back and allowing the negative propaganda to take a hold, instead of investing in the education of users globally and utilising the many available platforms to demonstrate how plastic has contributed to society in general through value engineered projects that provide significant environmental benefits and long-term reliability. Weholite is a spirally wound HDPE structured wall pipe that was developed in Finland in 1983 by KWH Pipe. It belongs to the Structured Wall Family that complies with International standards such as EN 13476, ISO 21138 and ASTM F894. The Technology is now owned by Uponor Infra Oy.

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Its purpose, just like all structured wall thermoplastic pipes is to specifically reduce the amount of plastic being used and to provide value and benefits to end users everywhere. In essence these products are environmental pioneers that should be exalted, not denigrated in a generic display of political correctness. The following case studies, featuring Weholite large diameter structured wall thermoplastic pipes, are an attempt to demonstrate those positive environmental and technical aspects that the general public are unaware of and that the plastics industry in its complacency has chosen to ignore.

Case Study 1 - Meadowhead CSO Attenuation Tank

Background For many years, coastal and inland waters the Irvine Bay area of Scotland have suffered from poor quality. Overflows from combined sewers (CSO) constituted a large part of the problem. To remedy the situation, the Meadowhead & Stevenston project was designed to significantly reduce the discharge from combined sewers in the towns of Kilmarnock and Irvine from spilling into the local river system in the event of heavy storms. In order to meet the European Directives on Bathing Water, Urban Waste Water and other mandatory standards, Scottish Water commissioned this project to ensure that their assets meet the required water quality. The CSO Attenuation Tank was only one section of the total project which improved the surface water quality for more than 80,000 people.

Several potential solutions There was a long history of potential solutions proposed for this section of the project. One of the alternatives was to construct a large diameter tunnel to provide in-line storm storage. This concept was deemed far too risky due to the extensive historically worked coal mine seams that underlie large areas of Kilmarnock. These mine workings are believed to date back to 1815, and most are uncharted, with their exact location and condition being unknown. This presented significant engineering challenges in terms of potential settlement beneath the tunnel and the risk of water and gas ingress during the tunneling works. This option was eventually ruled out on the basis that it was too expensive to treat all of the mine workings in order to construct the tunnel. The last option developed prior to the eventual Weholite solution involved construction of a rectangular, reinforced concrete, open-topped stormwater storage tank located on higher ground. However, the landowner objected to the sale of this land on the basis that the open tank significantly affected his potential to develop properties in the area.

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The final agreed solution had many benefits over the previous options. The underground CSO attenuation tank was constructed within the flood plain of the River Irvine, on land that had no development potential for the landowner. A buried tank leaves very little visual impact and allowed the landowner to return much of the land to agricultural use. For the Scottish Environmental Protection Agency

(SEPA), a buried tank was preferred since it did not take up any of the flood plain storage capacity. Also, there was no requirement for Planning Permission for the tank itself, because it is a below-ground structure. Following a tender process by Scottish Water, a joint venture between Morrison Construction and Black & Veatch (MBV) were awarded the project via a design and construct contract. Having assessed the initial designs MBV chose a Structured Wall HDPE pipe system (SWHDPE). A number of factors were paramount in that decision. SWHDPE has a smooth internal surface ensuring no need for expensive flushing and cleansing systems at the invert of the tank. This ensured low maintenance and essentially reduced whole life costs of the asset during its 100-year design life ensuring value for tax payers. The potential for a reduced programme time because of the ability to used factory-built components and very long, 15m pipe lengths. The ability of SWHDPE to behave homogeneously in very poor and unpredictable ground conditions and the fact that the solution would provide a fully tested 100% watertight system. The design solution offered by MBV using SWHDPE was instrumental in moving this part of the project forward into the delivery phase. MBV designed the system with an off-line storm storage tank, capable of holding 10 million litres of water.

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It was made up of approximately 2km of pipes - 16 x 96m long x DN2400 SN2 stiffness pipelines which were joined together at each end by prefabricated manifolds. The magnitude of the tank contains the rainwater during large storms before allowing flows through 200 metres of DN2100 SWHDPE pipes to a pumping station to be pumped through to Meadowhead Treatment Works once the storm has abated. After screening, the flow is then passed by gravity to a long sea outfall.

Installation in three months Compared with traditional reinforced concrete construction, SWHDPE Pipes were a more efficient alternative. As the construction was to take place in a flood plain, reduced programme time was crucial. Construction was scheduled in the drier spring and summer months to avoid the risk of the site flooding caused by the adjacent river. From initial excavation to completion of backfilling, the SWHDPE system was installed in three months. The original concept, the 100 m long x 60 m wide x 10 m deep concrete tank was scheduled to take 14 months to construct, which would significantly have increased the risk of

flooding and delayed the progress. Choosing SWHDPE also meant a smaller footprint on-site since the tank could be installed by a team comprising two excavators, three pipelayers, one engineer and two pipe welders. A reinforced concrete tank would have required up to 30 men, scaffolding, formwork, concrete, reinforcement, etc.

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With SWHDPE, site work was kept to a minimum as all of the prefabricated manifold sections were constructed in the factory. Other offsite designed sections included a number of access shafts on

the tank and at the bends on the approach pipes for inspection purposes. This negated the need to construct concrete inspection chambers, which offered further significant time and cost savings. The project won a number of health and safety awards. Using an SWHDPE system has led to the successful installation of one of the largest ever thermoplastic storage tanks anywhere in the world. As flooding in our urban environments continues to become more and more of a focus, plastic systems can will continue to be developed and utilised in order to meet environmental needs and alleviate the effects of climate change. “The Meadowhead and Stevenston project was, at the time, Scottish Water’s largest ever stormwater transfer scheme. Following a construction period of some 33 months, the construction of 12 miles of pipeline, three substantial new pumping stations, a 10,000m3 storage tank and several new Combined Sewer Overflow (CSO) structures significant environmental improvement to rivers in Kilmarnock and Irvine and to the coastal waters of Irvine Bay were recognised.”3

Case Study 2 - Petron Bataan Background4 Petron Corporation is the largest oil refining company in the Philippines with a combined refining capacity of 268,000-barrels-per-day. They supply nearly 40% of the country’s total fuel requirements through the operation of the 180,000-barrels-per-day oil refinery in Bataan. The facility refines crude oil into a full range of petroleum products including petrol, diesel, LPG, jet fuel, kerosene and petrochemicals.

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The Bataan Refinery (PBR) is the largest in the Philippines and is located within the Limay municipality of Bataan province. It was inaugurated in 1961 with a capacity of 25,000 barrels per day and it steadily grew to a rated capacity of 180,000 barrels-per-day. In 2011, Petron decided to develop the Refinery Expansion Project (RMP-2), in order to make the refinery more competitive in the Asia-Pacific region, by significantly increasing its production rate by up to 200% for some of their products. The expansion, which consisted of 19 additional processing units, was initiated in April 2011 and took 4 years to complete. The total estimated investment in the project is $1.8bn. Daelim of Korea were chosen as the Engineering, Procurement and Construction (EPC) Contractor, while CCT-Toyo of Japan carried out all associated tasks for the civil and marine works associated with the cooling water system. After initial concept meetings, the consortium very quickly chose to use a Structured Wall HDPE pipe system (SWHDPE) and brought in a team of experts from Uponor in Finland to oversee the design, delivery, installation and supervision of the system which included all of the intake and outfall pipelines, diffuser structures and the World’s first thermoplastic super-size intake structure, made from SWHDPE profile panels. Structured Wall HDPE Pipes and Panels can be easily welded together and do not corrode in the harsh salt water of marine applications.

Design and Analysis All the design work for the pipelines and structures was undertaken in Finland by Uponor Project Services. This included structural, hydraulic and mechanical design, modelling the submersion and FE Analysis of the intake structures and fittings, as well as all the drawings for the marine section of the project.

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The connecting pipelines were made up of 610m of 2400mm internal diameter pipes. The pipes were joined together in strings of 105m and submerged using the s-bend technique, utilising inflatable bags to control the sinking. The connection of the strings was done using uniquely designed flanges. The chlorination pipelines were also installed as part of the intake pipeline in order to assist with maintenance. In addition to the intake pipeline, there was a further 450m of 2200mm internal diameter pipes, installed as an outfall pipeline, using bespoke designed diffusers. The depth of submersion for both the intake and outfall pipelines was in the range of 12 to 18m.

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As part of the redevelopment, the World’s first thermoplastic super-size intake structure, made from a new patented concept known as Wehopanels - HDPE structured wall panels - was delivered. This system is lighter, faster to install, and therefore much better value than typical and traditional solutions for intake structures.

Installation The pipes were produced at a factory in Thailand and shipped by sea to the site, along with the specially designed flanges for jointing the strings of pipes together. In May 2013, the installation team mobilised from Finland and Thailand to the Philippines to start work at the Orion Port in Manila Bay, the site provided by CCT-Toyo for the welding activities and the launch of the Weholite strings. This type of Structured Wall HDPE Pipe was ideal for this complex marine installation for a number of reasons but probably the most important is that they eliminated the need for heavy concrete collars to ballast the strings. During the submersion process, control is of the utmost importance so the need to lower the risk level is vital. This team used a patented method of ballasting the

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strings by filling its hollow profile with an inexpensive and pumpable mortar and then killing the curing process. This gives the pipeline a number of advantages during and after the submersion. It provides around 20% extra weight to submerge the pipeline, whilst spreading the loads from the ballast evenly over the pipeline and as an extra advantage, it provides up to 33% extra stiffness to the pipeline. The profile filling takes place prior to the launching of the pipe strings. The submarine installation of this type of structure wall HDPE Pipes is faster than that of steel pipes and allowed the installation of over 200 linear metres a day. Since they do not require concrete collars, the contractors were able to use a smaller trench, which minimised the dredging operation. The reduced volume of excavations meant savings on cost and programme time. Construction costs of marine projects are far higher than land-based schemes. Although this was not the first time Structured Wall HDPE Pipes had been used for marine work in Asia, it was a milestone in the Philippines, it being the first time that it had been used as the lead material for an application of this kind.

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The Structured Wall HDPE system was chosen for its design life, 100 years. The material is non-corrosive and will enable Petron to avoid costly maintenance across its lifecycle.

Case Study 3 – Beckton Lee Tunnel Outfall Culvert Background London’s globally admired sewage system was created in the Victorian era by Sir Joseph Bazelgette. The water is carried through an elaborate network of interceptors. Essentially, it is a single combined system of storm and waste water which incorporates over 50 combined sewer overflows (CSOs) to both the Rivers Thames and Lee. This system now faces the challenges of ongoing urbanisation and ever-growing sewer discharges. It was designed to overflow into the River Thames during extreme weather, when the sewers reached capacity. One hundred and fifty years on, the system has outgrown the demands of an increasingly populated 21st century city, and sewer discharges are now happening much more frequently, around once a week on average, according to Thames Water and can even occur after as little as 2mm of rainfall. To combat this and in order to future-proof one of the world’s most populous cities, Thames Water has developed three major multi-billion pound engineering schemes to help prevent sewer overflows and improve water quality in the Thames. All five major sewage treatment works in London have undergone extensions and upgrades, the Lee Tunnel is in operation, and construction is underway on the Thames Tideway Tunnel. This will also ensure compliance with the European Union’s Urban Wastewater Treatment Directive (UWWTD).

The Lee Tunnel and Thames Tideway tunnel have the task of capturing an average of 39 million tonnes of sewage a year from the 35 most polluting combined sewer overflows (CSOs). An upgraded pipeline system was designed to reduce the number of overflows – and their environmental impact – from the sewers and treatment systems serving London. A particular aim is to limit pollution from the sewers and treatment systems connected to the Beckton STW on the Northside of the Thames and Crossness STW to the south.5

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The Project The £635M Lee Tunnel manages discharges from Abbey Mills Pumping Station in Stratford - London’s largest CSO - which accounts for 40% of the total discharge. At four miles long, the tunnel will run beneath the London Borough of Newham and will help prevent more than 16 million tonnes of sewage mixed with rainwater from overflowing into the River Lee each year. The new tunnel will capture the overflow and transfer it to Beckton Sewage Treatment Works, which has undergone vast extension work in order to deal with the increased volumes it will be processing.6

Picture – The Lee Tunnel System – Courtesy of Thames Water

Beckton STW, London.

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The construction of the Lee Tunnel brought with it a unique set of demands, the main one being the boring of London’s deepest ever tunnel, no small feat in a city that has one of the most complex subterranean networks in the world, creating something of a navigational and engineering headache. MVB, a joint venture between Morgan-Sindall, Vinci Construction Grand Projects and Bachy-Soletanche, were appointed as the principal contractor by Thames Water. In 2012, MVB approached Uponor Project Services together with the UK licensee Asset International Limited to examine the complex design. The original idea had included in-situ building a concrete box culvert in a dry trench by holding back the tidal waters of the Thames, which has a rise and fall of 7 metres.7 Construction work began in September 2010 and operations were completed in late 2015. The Beckton Overflow Shaft connects directly to the DN/ID3000 SWHDPE outfall pipeline and into the River Thames.

The Outfall Solution The Asset and Uponor PS partnership set about using their combined design expertise for land and marine applications to re-engineer the project by creating what is a landmark design, the biggest plastic outfall ever installed in Europe and one of the biggest in terms of diameter worldwide. The proposal to overcome this enormous challenge included 880 metres of 3000mm diameter SWHDPE pipes laid as a twin culvert along with twelve large-scale Wehopanel SWHDPE boxes, and the provision of installation, supervision, site services and health and safety management.

The initial design for the outfall culvert at Beckton, discharging water into Thames River, showed a concrete culvert as part of the design documentation, pre–stressed and fully exposed to aggressive water. Changing the culvert structure from concrete to a twin SWHDPE pipeline changed the design requirements completely. • The unit weight of culvert was reduced substantially • In the axial direction, the culvert is flexible, not rigid, and can take local settlements • There was no need for piling to support the culvert, only a gravel bedding

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Even though the thermoplastic pipeline has many advantages compared to the concrete culvert, the local conditions along the marine section, with a length of 335m, represented major challenges for the SWHDPE pipe, especially during the time of construction. It was clearly demonstrated that the selection of Structured Wall HDPE Pipes in SN4 stiffness to ISO 9969 were suitable for the installation and would meet the requirement of 120-year service life.

The Land Section Part 1 The project was divided into a land section comprising of 105m of twin culvert laid at 10m depths to invert. This section had the added complication of needing to break through the tidal protection wall that stops the Thames flooding Europe’s largest treatment works at Beckton. This issue was overcome by utilising a giant 7m x 11m x 5m Weholite HDPE Structured Wall Modular box to house a twin 3000mm spool section to complete the installation. However, this section would not be installed until the very end of the project.

The project started on the river side of the tidal protection wall. An extra wide trench was used in order to safely accommodate this section of the outfall which consisted of a twin pipeline 6 kN/m2

of 3000mm internal diameter. The length of the land part section was approximately 105m and the cover depth is 6.4m. The land section was connected with special flanges to the marine pipeline after its completion. The structural integrity of the twin pipeline was analysed using a number of calculation methods to ensure the confidence of the client who was using SWHDPE Pipes and Modular Boxes for the

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first time. Cande Finite Element Software was used for an additional check in the deflection values as well as the forces in the pipe perimetry of these particular pipes.

The results of the FE analysis illustrate that the deflection values for both pipes was approximately 2.5 %. This is well inside the acceptable limits and therefore there were no issues with the structural integrity of the pipes. These results were comparable with the other design methodologies that were utilised, namely, BS EN 1295 – 1: 1998, the Swedish calculation method and the vertical deflection values that were obtained by using the internal FE software of Uponor - ROR 99.

The backfill configuration consisted of a 500 mm granular bedding and granular backfill which was extended across the entire primary backfill zone and up to 500 mm above the crown of the pipe. The material used for the bedding and the primary backfill zone was single size stone to a maximum of 20 mm. This material is self-levelling and self-compacting and can flow around the critical areas of the pipes without any compaction effort especially in the haunch area below the spring-line. Native soil was used for the final backfill and to bring the trench to ground level. The water table was approximately 3.5 m below ground level. In theory, the water table reduced the

Granular bedding/backfill

Primary backfill zone

Native soil

Native soil

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load of the soil above the pipes, however in the simulation its effect of the was not taken into consideration and therefore it meant that the loading calculations were much more conservative than they needed to be.

The Marine Section The operation to install the remaining 335 metres of twin culvert section in the River Thames was carried out by marine contractor CMP, alongside the Asset and Uponor PS partnership. This ambitious marine project was further complicated by the fact that the pipes had to be submerged under an existing jetty structure and sections of the project were often isolated by the tide which, rises and falls by up to 7 metres in the Thames, with no access by land. The proposed outfall consisted of a twin pipeline DN/ID 3000 SN4 and a maximum cover depth of 2.2m.

Additionally, steel sheet piling of over 11,000m2 was installed to allow the riverbed to be dredged so that the pipes could be laid free of obstruction. Over 28,000m3 of riverbed materials were dredged, with much of the dredged material being reused to backfill the pipes once installed. This provided an environmental advantage based on vastly reducing the amount of materials taken off site and thereby reducing the carbon footprint.

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All the Structured Wall HDPE Pipes and Modular Boxes were manufactured and prefabricated at Asset’s South Wales factory. The pipes were delivered to the historic London Docks site in 18 metre lengths and were welded into strings of up to 90 metres. The strings, weighing 50 tonnes were then lifted onto the water using three mobile cranes in tandem and prepared for towing to the submersion site, at Beckton STW, around 3km upriver.

Part of this preparation involved utilising Uponor’s patented grouting process. This innovative methodology eliminates the need for heavy concrete collars to ballast the strings during submersion. This traditional way of installing marine pipelines carries extreme risk, especially during the submersion process. Filling the hollow profile with a grout is much safer, affords a much quicker preparation time and allows greater control during submersion. The process of profile filling results in a considerable increase in the stiffness of the pipe. In accordance with previous ring stiffness testing conducted on cement filled pipes of this specific type and done in accordance with ISO 9969: Thermoplastic Pipes - Determination of Ring Stiffness there is an increase in the ring stiffness value of the pipes of approximately 33%. However, for the purposes of a conservative safety factor, during calculations, the box is assumed hollow and the

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increased stiffness is ignored. The amount of self-deflection of the pipe due to the weight of concrete inside the hollow box section is approximately 1% of the inside diameter of the pipe.

When used in this way, the cement mortar is dosed with a retardant so that the hardening process is killed, and the strength of the mortar does not exceed 1 MPa. This means that the SWHDPE pipeline remains flexible and still carries all the advantages that HDPE usually provides for marine applications. With no concrete collars a smaller trench is needed, the dredging operation is minimised, and the volume of excavation is therefore drastically reduced. Since submarine excavations are much more expensive than on dry land the advantages of using SWHDPE pipes are transparent. By using this patented grouting system, the submersion is much easier to control and ultimately safer. Once the pipe strings were ready, they were towed individually upriver by tugboat. Care had to be taken to negotiate the pipe bridge across the submersion site and this meant that good timing was essential, especially with such a large tidal rise and fall.

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The strings were submerged using the horizontal beam method. A long airbag was inflated inside the pipeline and each end capped off. When the string was positioned correctly, water was allowed in at one end, air allowed out at the other whilst simultaneously the airbag was deflated. This allowed for a smooth and safe placement of the pipe string. Specialist divers were used to bolt the innovatively designed quick-connect flanges joining each pipe string

Each of the pipe strings were connected using a specially designed quick connect, conical flange made from galvanized steel with a high thickness coating. However, one of the specified criteria was a 120-year service life. Whilst this was not an issue for the SWHDPE pipes and modular boxes, a unique design had to be developed to protect the steel parts.

This consisted of each flange being placed inside SWHDPE modular boxes which consisted of 4 walls and a bottom plate. Each were welded together according to standard DVS 2207 methods. Once the steel parts were assembled the boxes were filled with liquid concrete to provide the necessary design life. The pipes were welded to the SWHDPE box on one side and additional anchoring into the concrete was provided by an HDPE puddle flange. Essentially the SWHDPE boxes were permanent formwork which also retained the concrete in position and protected it.

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The generated stress, shear and bending of the concrete blocks was calculated as being very close to zero, even without reinforcement, which supported the design life assumption of 120 years and the stress on the HDPE is also zero. Only the top of the concrete blocks were exposed to potential degradation from environmental attack. The concrete design followed the EU’s standard BS – EN 1991 -1-1 as well as Euro code 2.

The Land Section Part 2 – Installing ‘The Spool.’ The final piece of the jigsaw was the installation of the spool sections which were to bisect the tidal protection wall that prevents flooding of the whole of the Beckton STW.

This involved demolishing the wall and connecting the pre-installed pipes on either side of it using 3m long sections connected with a watertight mechanical coupling. The spool sections were situated inside the central box which had been installed midway between the main shaft and the marine connection.

The pre-installed pipes were heat fusion welded inside the SWHDPE modular boxes. When this operation had been completed the backfilling operation could commence. The blanking plates which had been welded inside the shoreside pipes were removed which allowed the waters of the Thames to flood the inside of the box.

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The spool sections were lowered into the box and connected using the watertight mechanical couplings which had stainless steel casings to a pre-determined torque setting. The pipes were then attached to prefabricated anchor points using nylon straps specially designed to counter the uplift forces initially from the water and eventually from the concrete infill. Once this final section was complete, the remaining backfill could be instated and the pipeline was ready for inspection and commission. It has now been in operation for the last five years. As well as servicing the Lee Outfall Tunnel, the Weholite culvert will also be the final discharge point for the prestigious £4.2BN Thames Tideway tunnel. Construction of this ‘super sewer’ started in 2014 and is scheduled to complete in 2020. The London Tideway improvements are but

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a few of the most impressive and ambitious engineering projects to be undertaken in the UK in a generation, perhaps since the Victorians themselves built the very sewers that Thames Water are currently upgrading. It is a fantastic example of world leading engineering at its best, and Structured Wall HDPE Pipes and Modular Boxes have been at the forefront. The scale and scope of this installation meant that not only did it become the UK’s largest thermoplastic outfall pipeline, but it also represented the UK’s first ever subsea installation of a sectional installed multi-directional sewage pipeline. References

1. https://www.theguardian.com/environment/2018/nov/13/the-plastic-backlash-whats-behind-our-sudden-rage-and-will-it-make-a-difference

2. https://www.independent.co.uk/topic/plastic-pollution 3. http://www.waterprojectsonline.com/case_studies/2013/Scottish_Meadowhead_2013.pd

f 4. https://www.petron.com/wp-content/uploads/2018/11/petron_ar2014.pdf 5. http://www.waterprojectsonline.com/case_studies/2016/online/thames_tideway_east_20

16.htm 6. https://www.geolsoc.org.uk/~/media/shared/documents/specialist%20and%20regional%2

0groups/EngineeringGroup/EGGS%20January%202014%20Presentation.pdf?la=en 7. http://www.waterprojectsonline.com/case_studies/2012/Thames_Lee_Tunnel_2012.pdf